1. Field of the Invention
The present invention relates generally to fiber optic couplers and particularly to a fiber optic coupler with an in-line optical component.
2. Description of the Related Art
In the field of fiber optics, it is often necessary to operate on an optical beam carried by an optical fiber using an optical component. For example, such optical components may include filters, such as colored glass, interference or neutral density filters, e.g. for blocking out or passing specific wavelengths of light, attenuators for reducing optical power to a desired range, polarizers for controlling the polarization of light, and isolators for preventing back reflections and other noise from reaching sensitive optical components. Such optical components are well known in the art.
A variety of “bench top” devices are known for use in a laboratory to set up optical components and fiber optic cables to allow access to and operation upon an optical beam. For example, Thor Labs of Newton, N.J., USA and Ocean Optics, Inc. of Dunedin, Fla., USA offer typical devices. These devices are adapted to position and hold a pair of fiber optic cables (and therefore fibers) in alignment at a specified distance from each other, e.g., approximately 1 to 2 inches. These devices include a structure permitting an optical component to be positioned therebetween to perform the desired operation on the optical beam after it exits the first fiber/cable and before it enters the second fiber/cable.
It will be appreciated that optical fibers provide for complete internal reflection of light and therefore there is little dissipation of light as it propagates along a continuous fiber. Where light dissipation will typically occur is at any interface between two mediums having different refractive indices, e.g. at a fiber/air interface, such as at the end of a single fiber or between two fibers held by a bench top device. Accordingly, as soon as the light leaves the first fiber and travels through the open air, the light begins to dissipate and/or diverge. This effect is significant even over the relatively short distance between the fibers when mounted in such bench top devices. Accordingly, each bench top device requires a pair of collimation lenses to focus the dissipating/diverging beam of light. In a bench top device, one such lens is positioned between each fiber and the optical component. These lenses are relatively expensive, typically costing hundreds of dollars and being the most expensive components in the bench top device.
There is a current trend toward the use of fiber optics in various pieces of equipment, and towards miniaturization of such equipment, e.g. to develop handheld devices. Such bench top devices are sufficiently large in size, e.g., approximately three inches by six inches by two inches, to be unsuitable for use in typical hand-held devices. The optical component is typically relatively large, e.g., greater than one-half inch square or approximately one inch round to account for inaccuracies in positioning of the fibers and/or optical component, and to facilitate handling. Such an arrangement is wasteful of optical component materials and contributes unnecessarily to the cost of the device.
Additionally, bench top devices require a high degree of precision in alignment of the fibers and optical component, and are therefore subject to a risk of misalignment due to jarring, etc. Some such devices have adjustments to permit realignment, but any realignment process requires an undesirable amount of work and time.
While some couplers with in-line optical components are known in the art, such couplers lack sufficient versatility to permit easy interchangeability of optical components and/or to allow for interchangeability of optical components of various thicknesses, particularly for connectors unlike the ST and FC connectors, which have floating, spring-biased designs and therefore have a degree of built-in versatility. Unlike telecommunications applications, which primarily involve long-term use of a pre-selected optical component in a given coupler, in spectroscopic applications, optical components must often be interchanged for a given coupler, e.g. when using a different sensor to perform a different analysis, or when analyzing a next, different substance.
What is needed is a compact, lens-free fiber optic coupler that provides for secure alignment of fibers, conservation of optical component materials, easy interchangeability of optical components, e.g. without the need for supplemental support structures such as bushings, sleeves or rings, and accommodation of interchangeable optical components of various thicknesses, and therefore various types.